High-frequency jet ventilation (HFJV) has been clinically demonstrated to be a useful tool in the management of major trauma and cardiopulmonary arrest, particularly as a practical method for emergency airway management in acute, uncontrolled settings. The positive pressure and airflow out of the oropharynx produced by the jet ventilator minimizes aspiration of gastric content, and the low airway pressures produced by HFJV tend to decrease the incidence of tension pneumothorax and impaired central venous return.
Prior art jet ventilators for medical purposes have used externally powered devices such as electric valves to produce the 1-15 Hz pulses of air or oxygen which are introduced into the patient's airway. For emergency use in the field, this is undesirable because of the need for batteries which tend to be heavy and to present reliability problems. In addition, electrical equipment can be dangerous in the presence of flammable fluids which are sometimes present in rescue situations.
It is known that cyclic fluidic pressure pulses can be produced through the use of an opposed vortex oscillator. In the past, such oscillators have been used as sensors for temperature, gas composition, or pressure ratio monitoring applications. In such uses, the oscillator system has a fixed geometry, and changes in the sensed gas parameters alter its frequency.
If an opposed vortex oscillator is used to control a jet ventilator, however, it is necessary for physiological reasons to control the frequency and also the duty cycle of the jet without altering the above parameters. It is with this requirement that the present invention is concerned.